Polystyrene-block-poly(2-cinnamoylethyl methacrylate) (PS-b-PCEMA) samples with n/m larger than 9.0, where n and m stand for the numbers of styrene and of CEMA units in a chain, formed essentially star micelles and those with n/m between 7 and 8.2 formed mixtures of star and long cylindrical micelles in cyclopentane with PCEMA as the core and PS as the shell. UV cross-linking of the PCEMA cores of these micelles at 50 degrees C yielded star polymers and nanofibers. This probably represents the first preparation of cross-linked block copolymer cylindrical micelles or nanofibers in the solution phase. While we have previously prepared star polymers using this approach, this study shows the robustness of this method in producing star polymers with as many as 4.5 x 10(2) arms and a molar mass of 9.9 x 10(7) g/mol. Detailed study showed that UV cross-linking only lacked in the structure of the micelles and did not change their aggregation numbers. This allowed us to determine the molar masses of the cross-linked micelles in toluene, in which uncross-linked micelles would have disintegrated, and to equate them to those of the uncross-linked micelles in cyclopentane. The aggregation numbers of the star micelles in cyclopentane were found to follow theoretical scaling laws.